In transportation systems in which vehicles are swept along within a conduit by a flowing stream of air, the manner in which the air is caused to flow within the system can affect certain characteristics of the system. For example, if the air flow is maintained by a series of spaced apart pumps which each withdraw a fraction of the system air and reintroduce it at locally increased velocity (i.e. as a jet) a continuous movement of the vehicles as they pass these jet pumps can be achieved but the pumping efficiency is relatively restricted. The pumping efficiency can be increased significantly by employing full flow pumps wherein each pump handles the air at a mass rate of flow somewhat in excess of that mass rate of flow at which the air is moving in the system. With a full flow pump system, however, a reverse flow air space is created in the conduit from the point at which air is re-introduced by the pump and to the point at which the air is withdrawn by the pump, creating regions at which the vehicles stop. Because of the intermittent nature of vehicular movements under these conditions, the full flow pump system with its concomitant high pumping efficiency has been considered to be of practical utility only in conjunction with a step-by-step program of vehicle movement through the system. Thus, a vehicle would stop at every pump station, "wait" for the next succeeding vehicle to arrive at that same station, and then be moved on for progression to the next station incident to the arrival of such succeeding vehicle, and so on through the system for as many vehicles as may be involved.
Because of the inherent capability for high pumping efficiency with full flow pump systems it would be desirable to provide such a system which also accommodates for continuous movement of the vehicles, as desired, through the system, i.e. is free from the restraint of step-by-step progression as aforesaid.